The present invention generally relates to a multiband data communication apparatus, a communication method of a multiband data communication apparatus, and a storage medium for storing a program used to execute the communication method of the multiband data communication apparatus. More specifically, the present invention is directed to a multiband data communication apparatus, a communication method of a multiband data communication apparatus, and a storage medium, capable of suppressing a circuit scale to a minimum circuit scale, and further capable of preventing a deterioration in a baseband signal.
As a conventional dual band data communication apparatus, or a conventional multiband data communication apparatus, one conventional data communication apparatus is represented in FIG. 12. That is, FIG. 12 is an arrangement diagram of a conventional multiband data communication apparatus. In this case, as the data communication apparatus, such a data communication apparatus is conceived as a mobile communication apparatus typically known as a digital portable telephone and a paging receiver.
This conventional multiband data communication apparatus is arranged by comprising an antenna 101, a local oscillator 104, a receiver unit, and a transmitter unit. In this apparatus, the receiver unit is provided with an RF (radio frequency) amplifier 102, a downconverter 103, an intermediate frequency amplifier 105, a quadrature demodulator 1208, and a data output circuit 1221, whereas the transmitter unit is provided with a (high power) power amplifier 602, an upconverter 603, a quadrature modulator 1218, and a waveform generating circuit 1222. Referring now to the multiband data communication apparatus shown in FIG. 12, the conventional technique will be described.
First, in the receiver unit, a modulated reception signal which is received by the antenna 101 is amplified by the RF amplifier 102, and thereafter the amplified reception signal is entered into the downconverter 103. The downconverter 103 may output such signals having frequencies which are defined by adding the frequency of the amplified reception signal to a frequency of a local oscillation signal 152 outputted from the local oscillator 104, and also by subtracting the frequency of the amplified reception signal from the frequency of the local oscillation signal 152. In this case, it is now assumed that while using either a low-pass filter or a high-pass filter, the downconverter 103 selects as a reception intermediate frequency signal 151, a signal having such a subtraction frequency lower than the frequency of the received RF signal. The reception intermediate frequency signal 151 having the frequency lower than the frequency of the reception signal, which is outputted from the downconverter 103 is amplified by the intermediate frequency amplifier 105. Then, the amplified intermediate frequency signal is entered into the quadrature demodulator 1208.
The quadrature demodulator 1208 is arranged by two sets of quadrature mixers 109 and 110, a reception local oscillator 111, and a phase shifter 1209. The quadrature mixers 109 and 110 convert the reception intermediate frequency signal into a reception baseband signal 157 and another reception baseband signal 158. The reception local oscillator 111 precisely outputs a signal having a carrier frequency equal to a central frequency of the reception intermediate frequency signal. The phase shifter 1209 produces two signals 155 and 156 whose phase difference is 90 degrees from the reception local signal, and then enters both the signals 155 and 156 into the quadrature mixers 109 and 110.
The quadrature demodulator 1208 enters thereinto the amplified reception intermediate frequency signal, and then outputs two sets of reception baseband signals 157 and 158 whose phase difference is 90 degrees. The data output circuit 1221 decodes reception data 159 by utilizing a phase relationship between the reception baseband signals 157 and 158 having the phase difference by 90 degrees from each other.
Next, a description will now be made of operations of the receiver unit having the quadrature demodulator 1208 equipped with the above-explained function.
In general, assuming now that orthogonal baseband signal components are I(t) and Q(t), and an angular frequency of a carrier wave is “ωRF”, a reception signal SRF(t) may be expressed by the following formula (1):SRF(t)=I(t)cos[ωRFt]+Q(t)sin[ωRFt]  (1)It should be noted that a coefficient of an amplitude which is equally applied to the respective terms of the below-mentioned formulae is negligible.
Also, assuming now that an angular frequency of a local oscillation signal is “ωL0” and an arbitrary phase difference is “ØL0”, an output signal “SL0(t)” of the local oscillator 104 which is entered into the downconverter 103 is expressed by the following formula (2):SL0(t)=cos[ωL0t+ØL0]  (2)
In the downconverter 103, the reception signal SRF(t) is multiplied by the local oscillation signal SL0(t), so that an output SMIX(t) of the downconverter 103 is given by the following formula (3):
                                                                        SMIX                ⁡                                  (                  t                  )                                            =                            ⁢                                                SL0                  ⁡                                      (                    t                    )                                                  ·                                  SRF                  ⁡                                      (                    t                    )                                                                                                                          =                            ⁢                                                I                  ⁡                                      (                    t                    )                                                  ⁢                                  {                                                            cos                      ⁡                                              [                                                                                                            (                                                                                                ω                                  ⁢                                                                                                                                          ⁢                                  L0                                                                +                                                                  ω                                  ⁢                                                                                                                                          ⁢                                  RF                                                                                            )                                                        ⁢                            t                                                    +                                                      ∅                            ⁢                                                                                                                  ⁢                            L0                                                                          ]                                                              +                                                                                                                                                          ⁢                                  cos                  ⁡                                      [                                                                                            (                                                                                    ω                              ⁢                                                                                                                          ⁢                              L0                                                        -                                                          ω                              ⁢                                                                                                                          ⁢                              RF                                                                                )                                                ⁢                        t                                            +                                              ∅                        ⁢                                                                                                  ⁢                        L0                                                              ]                                                  }                            +                                                                                        ⁢                                                Q                  ⁡                                      (                    t                    )                                                  ⁢                                  {                                                            sin                      ⁡                                              [                                                                                                            (                                                                                                ω                                  ⁢                                                                                                                                          ⁢                                  L0                                                                +                                                                  ω                                  ⁢                                                                                                                                          ⁢                                  RF                                                                                            )                                                        ⁢                            t                                                    +                                                      ∅                            ⁢                                                                                                                  ⁢                            L0                                                                          ]                                                              +                                                                                                                                        ⁢                              sin                ⁡                                  [                                                                                    (                                                                              ω                            ⁢                                                                                                                  ⁢                            L0                                                    -                                                      ω                            ⁢                                                                                                                  ⁢                            RF                                                                          )                                            ⁢                      t                                        +                                          ∅                      ⁢                                                                                          ⁢                      L0                                                        ]                                            }                                                          (        3        )            
Also, since the term of “ωL0+ωRF” of the output of the downconverter 103 corresponding to the high frequency component is negligible in either the low-pass filter or the high-pass filter, when ωL0>ωRF, the reception intermediate frequency signal SIF(t) (151) may be expressed by employing this angular frequency ωIF (=ωL0−ωRF):SIF(t)=I(t)cos[ωIFt+ØL0]−Q(t)sin[ωIFt+ØL0]  (4)
In the quadrature demodulator 1208, the reception baseband signals 157 and 158 are obtained by multiplying this reception intermediate frequency signal SIF(t) by the reception local oscillation signals 155 and 156 whose phase difference is 90 degrees. Assuming now that the reception baseband signals 157 and 158 correspond to “a(t)” and “b(t)”, respectively, these baseband signals are expressed as follows:
                                                                        a                ⁡                                  (                  t                  )                                            =                            ⁢                                                SIF                  ⁡                                      (                    t                    )                                                  ⁢                                  cos                  ⁡                                      [                                                                  ω                        ⁢                                                                                                  ⁢                        IFt                                            +                                              ∅                        ⁢                                                                                                  ⁢                        IF                                                              ]                                                                                                                          =                            ⁢                                                                    I                    ⁡                                          (                      t                      )                                                        ⁢                                      {                                                                  cos                        ⁡                                                  [                                                                                    2                              ⁢                              ω                              ⁢                                                                                                                          ⁢                              IFt                                                        +                                                          ∅                              ⁢                                                                                                                          ⁢                              L0                                                        +                                                          ∅                              ⁢                                                                                                                          ⁢                              IF                                                                                ]                                                                    +                                              cos                        ⁡                                                  [                                                                                    ∅                              ⁢                                                                                                                          ⁢                              L0                                                        -                                                          ∅                              ⁢                                                                                                                          ⁢                              IF                                                                                ]                                                                                      }                                                  -                                                                                                      ⁢                                                Q                  ⁡                                      (                    t                    )                                                  ⁢                                  {                                                            sin                      ⁡                                              [                                                                              2                            ⁢                            ω                            ⁢                                                                                                                  ⁢                            IFt                                                    +                                                      ∅                            ⁢                                                                                                                  ⁢                            L0                                                    +                                                      ∅                            ⁢                                                                                                                  ⁢                            IF                                                                          ]                                                              +                                          sin                      ⁡                                              [                                                                              ∅                            ⁢                                                                                                                  ⁢                            L0                                                    -                                                      ∅                            ⁢                                                                                                                  ⁢                            IF                                                                          ]                                                                              }                                                                                        (        5        )            
In this case, since the baseband component is derived by neglecting the high frequency component, the reception baseband signal “a(t)” (157) is eventually given as:a(t)=I(t)cos[ØBB]+Q(t)sin[ØBB]  (6)
In this formula, it is assumed that ØBB=ØIF−ØL0.
Similarly, since the other reception baseband signal “b(t)” is equal to SIF(t) sin [ωIFt+ØIF], this baseband signal “b(t)” is expressed as follows:b(t)=I(t)sin[ØBB]+Q(t)cos[ØBB]  (7)While utilizing the quadrature characteristic of the signals, the respective components I(t) and Q(t) can be derived.
In this case, it is set that ωL0>ωRF. However, such a frequency relationship cannot always be established in such a circuit arrangement capable of handling a plurality of frequency bands called as either “dual band” or “multiband”. In other words, in a certain frequency band, the frequency relationship ωL0>ωRF may be established and thus, the above-explained formulae can be calculated. However, considering now that another frequency relationship ωL0<ωRF is established in another frequency band, since ωIF=ωRF−ωL0, the following formulae are given as follows:SIF2(t)=I(t)cos[ωIFt−ØL0]+Q(t)sin[ωIFt−ØL0]  (10)a2(t)=I(t)cos[ØBB2]−Q(t)sin[ØBB2]  (11)b2(t)=I(t)sin[ØBB2]−Q(t)cos[ØBB2]  (12)As a result, reception baseband signals whose phase relations are different from each other are obtained.
In such a case, in the data output circuit 1221, the polarities of the reception baseband signals 157 and 158 are switched by employing the band switching signal 153. As a result, similar reception data 159 may be obtained.
On the other hand, in the transmitter unit, the waveform producing circuit 1222 into which transmission data 659 is inputted produces both a transmission baseband signal 657 and another transmission baseband 658, which may have a phase relationship in accordance with the entered transmission data 659. Then, the waveform producing circuit 1222 enters the transmission baseband signals 657 and 658 to the quadrature modulator 1218.
The quadrature demodulator 1218 is arranged by two sets of quadrature mixers 609 and 610, a transmission local oscillator 611, and a phase shifter 1219, and also an adder 606. The quadrature mixers 609 and 610 convert the transmission baseband signals 657 and 658 into the intermediate frequency signals. The transmission local oscillator 611 precisely outputs a signal having a carrier frequency equal to a central frequency of the intermediate frequency signal. The phase shifter 1219 produces two signals 655 and 656 whose phase difference is 90 degrees from the transmission local signal, and then enters both the signals 655 and 656 into the quadrature mixers 609 and 610. The adder 606 adds two sets of intermediate frequency signals outputted from two sets of the quadrature mixers 609 and 610 to each other, and then outputs a transmission intermediate frequency signal.
The quadrature 1218 enters thereinto both the transmission baseband signals 657 and 658 which own a phase difference in accordance with the transmission data 659, and then outputs a transmission intermediate frequency signal 651. The upconverter 603 outputs signals having frequencies obtained by adding and subtracting the frequency of the entered transmission intermediate frequency signal 651 and the frequency of the entered local oscillation signal 152. However, in this case, while employing either a high-pass filter or a band-pass filter, this up-converter 603 selects such a signal having a summation frequency higher than the original frequency as a transmission RF signal. The transmission RF signal derived from the upconverter 603 is amplified by the (high power) power amplifier 602, and then the amplified power transmission RF signal is outputted from the antenna 101 as the transmission signal.
Next, a description will now be made of operations of the transmitter unit including the quadrature modulator 1218 equipped with the above-explained function.
Generally speaking, in the waveform generating circuit 1222, assuming now that the transmission baseband signals 657 and 658 which own an orthogonal phase relationship between them and are produced from the transmission data 659 are expressed as an “I(t)” and a “Q(t)”, respectively, and also an angular frequency of a local oscillation signal outputted from the transmission local oscillator 611 is equal to “ωIF”, the transmission intermediate frequency signal 651 may be expressed as follows:SIF(t)=I(t)cos[ωIFt]+Q(t)sin[ωIFt]  (18)It should be noted that a coefficient of an amplitude equally applied to the respective items is negligible.
In the upconverter 603, assuming now that the output signal of the upconverter 603 which is obtained by being multiplied by the output signal SL0(t) of the local oscillator 104 is equal to SMIX(t), this transmission intermediate frequency signal 651 is given as follows:
                                                                        SMIX                ⁡                                  (                  t                  )                                            =                            ⁢                                                SL0                  ⁡                                      (                    t                    )                                                  ·                                  SIF                  ⁡                                      (                    t                    )                                                                                                                          =                            ⁢                                                cos                  ⁡                                      [                                                                  ω                        ⁢                                                                                                  ⁢                        L0t                                            -                                              ∅                        ⁢                                                                                                  ⁢                        L0                                                              ]                                                  ×                                  {                                                                                    I                        ⁡                                                  (                          t                          )                                                                    ⁢                                              cos                        ⁡                                                  [                                                      ω                            ⁢                                                                                                                  ⁢                            IFt                                                    ]                                                                                      +                                                                  Q                        ⁡                                                  (                          t                          )                                                                    ⁢                                              sin                        ⁡                                                  [                                                      ω                            ⁢                                                                                                                  ⁢                            IFt                                                    ]                                                                                                      }                                                                                                        =                            ⁢                                                I                  ⁡                                      (                    t                    )                                                  ⁢                                  {                                                            cos                      ⁡                                              [                                                                                                            (                                                                                                ω                                  ⁢                                                                                                                                          ⁢                                  L0                                                                -                                                                  ω                                  ⁢                                                                                                                                          ⁢                                  IF                                                                                            )                                                        ⁢                            t                                                    +                          ∅L0                                                ]                                                              +                                                                                                                                                          ⁢                                  cos                  ⁡                                      [                                                                                            (                                                                                    ω                              ⁢                                                                                                                          ⁢                              L0                                                        -                                                          ω                              ⁢                                                                                                                          ⁢                              IF                                                                                )                                                ⁢                        t                                            +                                              ∅                        ⁢                                                                                                  ⁢                        L0                                                              ]                                                  }                            +                                                                                        ⁢                                                Q                  ⁡                                      (                    t                    )                                                  ⁢                                  {                                                            sin                      ⁡                                              [                                                                                                            (                                                                                                ω                                  ⁢                                                                                                                                          ⁢                                  L0                                                                -                                                                  ω                                  ⁢                                                                                                                                          ⁢                                  IF                                                                                            )                                                        ⁢                            t                                                    +                                                      ∅                            ⁢                                                                                                                  ⁢                            L0                                                                          ]                                                              -                                          sin                      ⁡                                              [                                                                                                            (                                                                                                ω                                  ⁢                                                                                                                                          ⁢                                  L0                                                                -                                                                  ω                                  ⁢                                                                                                                                          ⁢                                  IF                                                                                            )                                                        ⁢                            t                                                    +                                                      ∅                            ⁢                                                                                                                  ⁢                            L0                                                                          ]                                                                              }                                                                                        (        19        )            
Only such a desirable frequency component of the signal outputted from the upconverter 603 is selected. In the case that the local frequency is higher than the transmission frequency, assuming now that an angular frequency of a transmission signal SUL(t) is equal to ωRF (=ωL0−ωIF), this transmission signal SUL(t) is given as follows:SUL(t)=I(t)cos[ωRFt+ØL0]−Q(t)sin[ωRFt+ØL0]  (20)
However, in such a case that the local frequency lower than the transmission frequency, the angular frequency of the transmission signal becomes ωRF=ωL0+ωIF, and thus this transmission signal SLL(t) is given as follows:SLL(t)=I(t)cos[ωRFt+ØL0]+Q(t)sin[ωRFt+ØL0]  (21)As a result, this transmission signal SLL(t) may become a different transmission signal, depending upon the frequency relationship between the transmission signal and the local signal.
Accordingly, in such a case, in the waveform generating circuit 1222, the polarities of the reception baseband signals 657 and 658 are switched by employing the band switching signal 153, and furthermore, for instance, “Q(t)” is replaced by “−Q(t)” in the above-explained formula, so that a similar transmission signal can be obtained.
However, in the circuit arrangement of the above-explained conventional multiband data communication apparatus for switching the polarity of the baseband signal, a large circuit scale requirement is further made as to both the data output circuit 1221 and the waveform generating circuit 1222 which originally own the large circuit blocks. Moreover, there is another problem that since such a circuit is additionally provided, the signal quality of such a low-noise baseband signal would be deteriorated.